JPH02114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for non-pollutingly treating hazardous wastes containing heavy metals such as municipal waste and industrial waste.

Generally, the residue and dust discharged when municipal waste, sludge, etc. produced from wastewater treatment processes are incinerated contain various harmful heavy metals. However, there is no established treatment method for waste such as dust that contains these harmful heavy metals, and the current situation is that it is simply dumped in landfills. There are concerns that heavy metals will leach out in rainwater and contaminate the environment around the landfill.

For example, when examining the chemical properties of waste such as dust generated during the incineration of municipal waste, we find that dust contains large amounts of water-soluble salts in addition to water-insoluble oxides.

The main forms of oxides contained in the dust etc. are SiO ₂ , Al ₂ O ₃ and CaO, and the salts are
It must be a salt of an alkali metal or alkaline earth metal such as NaCl, KCl, CaCl ₂ , Na ₂ SO ₄ , K ₂ SO ₄ (hereinafter abbreviated as alkali (earth) metal salt).

In addition, harmful heavy metals (e.g. Cd, Pb,
Most of Zn, Cu, Hg) are also in the form of heavy metal salts, such as chlorides or sulfates.

However, even if attempts are made to harden dust containing large amounts of salts by directly adding cement to the dust using conventional methods to immobilize heavy metals, the dust containing large amounts of salts for,
The solidification reaction of cement is inhibited and the strength of the solidified product is low, and if it is exposed to rainwater in a landfill, it will disintegrate, causing re-leaching of heavy metals and making it impossible to achieve the purpose.

As described above, wastes such as dust containing large amounts of alkali (earth) metal salts and heavy metals in the form of salts were extremely polluting and posed problems in treatment.

As a means to prevent the elution of heavy metals from these highly polluting wastes such as dust, the present inventor has already proposed in Japanese Patent Application No. 144620/1983 that the dust is dissolved only in an alkaline aqueous solution without adding iron salts, and then mixed with a liquid. We propose a method of separating the residue and discharging the liquid or evaporating and concentrating it to recover the alkali (earth) metal salts contained in the liquid, while the residue containing heavy metals is solidified with cement and disposed of. . However, although the solidified material created using this method did not elute heavy metals in near-neutral water, large amounts of heavy metals were observed to elute when it came into contact with acidic water. That is, heavy metals cannot be considered to be completely stabilized by this method. Also, depending on the type of waste, heavy metals may be detected in the liquid, which may hinder the recovery of alkali (earth) metal salts, or
In addition, if the water is discharged without being collected, it may cause secondary pollution.

The present invention further solves these problems, enables hazardous waste containing heavy metals to be dumped without any problem under any conditions, proposes a more stable method for preventing heavy metal elution, and at the same time proposes a method for preventing the elution of heavy metals. The purpose is to provide an effective method for recovering harmless valuable materials that do not contain heavy metals in an inexpensive form.

The present invention provides 2 parts (by weight) of pulverized waste or pulverized waste containing hazardous heavy metals and salts of alkali metals and/or salts of alkaline earth metals.
~10 parts of water is added to form a slurry, and 5 parts of the total number of moles of harmful heavy metal ions dissolved in the slurry are added.
~50 times as much iron ion is added, then an alkaline substance or its aqueous solution is added to adjust the pH of the slurry to 5 or higher, and the slurry is separated into liquid and residue by passing through, and cement is added to the resulting residue. This is a method for treating waste containing hazardous heavy metals, which is characterized by mixing and solidifying.

That is, in the present invention, waste containing heavy metals is pulverized, or the pulverized waste containing heavy metals is immersed in water to remove heavy metal salts and alkali (earth) metal salts contained in the waste. While dissolving, the added iron salt and the dissolved heavy metal salt are converted into hydroxide by added alkali, which is then separated into a liquid and a residue by passing through it, and further, cement is added to this residue. This is a processing method to form a solidified product.

One embodiment of the present invention will be explained with reference to the drawings. First, waste A such as dust is put into a water tank B, immersed in water to form a slurry, and a water-soluble alkali (earth) metal salt and a heavy metal salt are mixed together. Dissolve in water. Next, when iron salt C and alkali D are added to the slurry, the heavy metal salt in the dust and the added iron salt become hydroxides and become insoluble. On the other hand, the alkali (earth) metal salts in dust do not form hydroxides, so they are dissolved as they are, and oxides are originally insoluble, so they remain suspended, and the heavy metal hydroxides, iron hydroxides, etc. It becomes a suspended slurry in a mixed state. Next, after the slurry is sedimented, it is further filtered through filter E to perform solid-liquid separation, and the liquid F side contains NaCl, KCl,
Alkali (earth) metal salts such as CaCl ₂ , Na ₂ SO ₄ , K ₂ SO ₄ migrate, and heavy metal hydroxides, iron hydroxides, SiO ₂ , Al ₂ O ₃ , CaO, etc. Oxides remain in a mixed state.

On the other hand, NaCl, KCl, which moved to the liquid F side,
The solution 1 containing alkali (earth) metal salts such as CaCl ₂ , Na ₂ SO ₄ , K ₂ SO ₄ etc. is recovered by evaporation and concentration in an evaporator H, and then used as a non-hazardous industrial solution in place of potash or rock salt. It can be used as raw material 2 for fertilizers.

In this embodiment, iron hydroxide, which has good sedimentation properties, and heavy metal hydroxide, which has poor sedimentation properties, are precipitated in a mixed state, and then over-separated. Because it is incorporated or adsorbed and precipitated, the precipitation rate is faster than that of heavy metal hydroxide alone, and its permeability is also good. Furthermore, the iron hydroxide also has the ability to adsorb heavy metal ions, and because the solubility of the hydroxide also adsorbs dissolved heavy metal ions and precipitates, it can completely prevent heavy metal ions from migrating to the liquid side. .

The heavy metals contained in the mixture 3 of heavy metals, iron, and oxides on the excess residue G side have been converted into a form that is insoluble even in acidic water, so there is no problem if they are dumped as is in a landfill. In order to improve handling during continuous transportation and ground stability of the landfill,
Further, cement K is added and mixed in a solidifying device I to form a solidified product 4 having high mechanical strength. In other words, alkali (earth) has a negative effect on cement K.
Most of the metal salts migrate to the liquid F side, and the salt content remaining in the mixture is extremely small, so that it can be solidified with cement K.

In this process, the reason why the heavy metals in the above mixture are stable even in acidic water is that due to the coexistence of iron ions and alkali in the heavy metal ions, mixed hydroxides of heavy metals and iron are generated, and at this point, the heavy metals in the mixture are stable even in acidic water. It is assumed that this is because heavy metals are incorporated into the crystal lattice of iron hydroxide, or heavy metal hydroxides are adsorbed to iron hydroxide, ultimately creating a very stable crystal structure of iron and heavy metals. .

In the series of steps in the present invention, when dissolving waste such as dust in water, the ratio of waste to water is [Water/waste (weight)] ranges from 2 to 10. In order to mix and solidify the excess residue and cement, it is possible to solidify the cement by dissolving and removing the salt concentration in the residue to 50% or less, preferably 30% or less, and the solidified product after disposal. does not disintegrate, but this condition is satisfied if the waste is treated at the above-mentioned ratio of waste and water.

In addition, iron salts added to the slurry include ferrous sulfate (FeSO ₄ ), ferric sulfate (Fe ₂ SO ₄ ) ₃ ), ferrous chloride (FeCl ₂ ), and ferric chloride (FeCl ₃ ). In addition to these chemicals, ferrous chloride and ferrous sulfate, which are by-products produced in large quantities during the pickling of iron plates and the production of titanium oxide, can also be used. Further, as the alkali, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) ₂ ), ammonium hydroxide (NH ₄ OH), etc. can be used alone or in combination. .

In the present invention, the amount of the iron salt added varies depending on the type and amount of the dissolved toxic heavy metal, the pH after adding the alkali, etc., but it has been confirmed through experiments that the amount of the iron salt added is 5 to 50 of the total number of moles of harmful heavy metal ions dissolved in the slurry
It's double. Further, the amount of alkali added is set to such an amount that the pH of the slurry is adjusted to 5 or more, preferably in the range of 8 to 12.

That is, when the pH reaches 5 or more, the amount of heavy metals transferred to the liquid begins to decrease, and at a pH of 8 to 12, the heavy metals are hardly detected in the liquid.

Furthermore, when waste such as dust is discharged from an incineration facility, the liquid may be evaporated using waste heat J, for example, waste gas, of the incineration facility.

In addition, since the liquid does not contain harmful heavy metals, it is possible to discharge the alkali metal salts as they are without recovering them.Furthermore, when waste such as dust is discharged from an incineration facility, It is also possible to absorb the liquid into the incinerated ash discharged from the incinerator body, which does not contain any moisture and may be scattered during handling, and then dispose of it.

According to the method of the present invention, harmful and unstable heavy metal salts are converted into stable forms and then disposed of, while harmless and valuable alkali (earth) metal salts are efficiently separated and collected. This has the useful benefit of making it possible to accurately prevent heavy metal elution.

Next, examples of the present invention will be shown.

Alkali (earth) metal salts 80% (NaCl23.3%,
KCl 9.5%, Na ₂ SO ₄ 11.0%, K ₂ SO ₄ 33.0%,
CaCl ₂ 3.2%), insoluble oxides 10% (SiO ₂ 3.3
%, Al ₂ O ₃ 1.5%, CaO 3.0%, MgO 2.2%) 1 kg of electrostatic precipitated dust from a municipal waste incineration plant was dissolved with 4 ml of water to make a slurry. As a result, a total of 0.1 mol of harmful heavy metals Zn, Cd, and Pb were dissolved in this slurry. Next, 0.5 mol of FeSO ₄ was added and stirred, and then the pH of the slurry was adjusted to 10.0 using Ca(OH) ₂ and stirred again to form a mixture consisting of heavy metal hydroxide, iron hydroxide, and the above-mentioned oxides. It was created. This mixture was then passed through a filter press. Zn, Cd, Pb in the liquid at this time
Ion analysis revealed that Zn, Cd, and Pb were 0.01 ppm, 0.02 ppm, and 0.01 ppm, respectively, and the concentration of alkali (earth) metal salts in the excess residue had decreased to 30%.

Next, 50% (based on the dried residue) of cement was added to the residue passed through the filter press and kneaded to form a solidified product. As a result of curing this solidified product for one week, it was a strong solidified product with a crushing strength of 42 kg/cm ² and did not disintegrate even when submerged in water.

Furthermore, as a result of an elution test of this solidified material with water at pH 7 following the elution test method for hazardous wastes notified by the Environment Agency, all of Cd, Pb, and Zn were ND (0.001 ppm or less), so there is no problem even if it is disposed of. Hanakatsuta (regulatory value
There are no regulatory values for Cd0.3ppm, Pb3ppm, and Zn). Also,
In order to examine the leachability of heavy metals in acidic conditions,
Using the sample, an elution test was conducted in a solution controlled at PH4. As a result, the heavy metal concentrations in the eluate were Cd0.1ppm, Pb0.5ppm, Zn0.3ppm,
Even in acidic conditions, the regulatory values were fully satisfied.

On the other hand, as a result of evaporating and concentrating the liquid, NaCl,
An extremely pure white mixture of KCl, Na ₂ SO ₄ and K ₂ SO ₄ was obtained.

[Brief explanation of drawings]

The drawings are system explanatory diagrams showing embodiments of the present invention. A...Waste, B...Aquarium, C...Iron salt, D...
...alkali, E...filtration device, F...liquid, G...
...excess residue, H...evaporation device, I...solidification device,
J...Waste heat, K...Cement, 1...Alkali (earth) metal salt-containing solution, 2...Raw material, 3...Mixture, 4...Solidified product.

Claims (1)

[Claims] 1 Add 2 to 10 parts of water to 1 part (by weight) of pulverized waste or pulverized waste containing hazardous heavy metals and salts of alkali metals and/or salts of alkaline earth metals to form a slurry. Then, iron ions are added in an amount of 5 to 50 times the total number of moles of harmful heavy metal ions dissolved in the slurry, and then an alkaline substance or its aqueous solution is added to adjust the pH of the slurry to 5 or more, and then this is filtered. A method for treating waste containing hazardous heavy metals, which comprises separating the waste into a liquid and a residue, adding cement to the resulting residue, and solidifying the mixture.